1. Field of the Invention
The present invention relates to a semiconductor memory device and a data write method thereof, and is applied, for example, to a NAND flash memory.
2. Description of the Related Art
In a data write operation of a NAND flash memory, for example, a program loop is repeated with an arbitrary step width, and the program loop is stopped when data write in all bits is finished.
With the development of multilevel implementation of NAND flash memories, it becomes necessary to more finely control the intervals of data write levels of memory cells. It is thus necessary to make a write step voltage (dVPGM) lower. However, the decrease in write step voltage (dVPGM) leads to an increase in the number of times of data write, that is, an increase in program time (tPROG).
In the market in recent years, there has been a stronger demand for higher-speed, larger-capacity memories. In this trend, one problem is how to shorten a write time, while ensuring reliability.